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Biomedical subjects

J W Wood

Publications and source records attributed to J W Wood.

At least 19 recordsLinked to original sources
PubMed2006

Ovulation detection methods for urinary hormones: precision, daily and intermittent sampling and a combined hierarchical method.

BACKGROUND: We evaluate the performance of ovulation detection methods and present new approaches, including evaluation of methods for precision, combining multiple markers into a hierarchical system and using ovulation markers in intermittent sampling designs. METHODS: With serum LH peak day as the 'gold standard' of ovulation, we estimated accuracy and precision of ovulation day algorithms using 30 ovulatory menstrual cycles with daily urinary and serum hormones and transvaginal ultrasound. Sensitivity and specificity for estimating the presence of ovulation were tested using visually assessed ovulatory (30) and anovulatory (22) cycles. RESULTS: Sensitivity and specificity ranged from 70 to 100% for estimating presence of ovulation with twice-per-cycle, weekly, twice weekly, every-other-day and daily specimens. A combined hierarchical method estimated ovulation day using daily specimens within +/-2 days of the gold standard in 93% of cases. Accuracy of estimating ovulation day within +/-2 days using intermittent sampling ranged from 40% (weekly sampling) to 97% (every-other-day). CONCLUSIONS: A combined hierarchical algorithm using precise and accurate markers allows maximal use of available data for efficient and objective identification of ovulation using daily specimens. In intermittent sampling designs, the presence and the timing of ovulation can be estimated with good sensitivity, specificity and accuracy.

Adult↗
PubMed1998

Declining fecundity and ovarian ageing in natural fertility populations.

Worldwide, human fertility declines with increasing maternal age, after contraceptive-use patterns and behavioral factors are taken into consideration. Here, we summarize some of our theoretical and empirical work examining the biological factors contributing to this age pattern of fertility. We undertook an 11 month prospective endocrinological study in a natural fertility (non-contracepting) population (rural Bangladesh) to estimate the contributions of fetal loss and fecundability (the probability of conception) to declining fecundity with age. Prospective interviews and urine samples for pregnancy tests were collected twice weekly from up to 700 women. These data were used to test mathematical models of the underlying biological processes contributing to changing fecundability and fetal loss risk with maternal age. The results indicate that much of the decline in fecundity can be attributed to an increasing risk of fetal loss with maternal age. Much of this fetal loss is due to chromosomal abnormalities--a result of ageing oocytes. Fecundability, on the other hand, does not begin to decline until the early 40s. We hypothesize that this is also a result of ageing at the ovarian level, namely follicular atresia, in the years just prior to menopause. The irregularity of menstrual cycles--longer cycles and increasingly variable hormonal patterns--at these ages may be a direct result of the small and rapidly dwindling remaining pool of follicles. We present a simple mathematical model of this process, and some preliminary laboratory results that support the model.

Adult↗
PubMed1997

The evaluation of delayed-type hypersensitivity responsiveness and nutritional status as predictors of gastro-intestinal and acute respiratory infection: a prospective field study among traditional nomadic Kenyan children.

A 10-month prospective study of children from a nomadic pastoralist community in northwest Kenya was conducted to examine the relationship between nutritional status, cell-mediated immunity (CMI), and morbidity due to gastroenteritis and acute respiratory infection (ARI). In children ages 6 months to 10 years, nutritional status and cellular immunocompetence, determined by delayed-type hypersensitivity (DTH), were related to individual attack rates of diarrhoea and ARI over two 5-month observation periods, one each in the wet and dry season. While no association was found between premorbid nutritional status and gastroenteritis, DTH responsiveness was a significant predictor of diarrhoeal disease, with anergic children experiencing, on average, 20 per cent higher attack rates than immunocompetent children. When examined separately, both nutritional status and DTH responsiveness were significant predictors of individual attack rates of ARI in the wet season. However, when the effects of nutritional and immunological status were simultaneously tested, only DTH responsiveness was significant. Anergic children experienced 34 per cent excess ARI, compared to immunocompetent children. These results indicate that cellular immunocompetence is a sensitive predictor of gastrointestinal and respiratory infection, and that the effect of nutritional status on the occurrence of ARI may be mediated by cellular immune function.

Child↗
PubMed1994

Proportional hazards analysis of diarrhea due to enterotoxigenic Escherichia coli and breast feeding in a cohort of urban Mexican children.

Ninety-eight women-infant pairs were followed for up to 50 weeks in the northern part of Guadalajara, Mexico, from August 1986 to July 1987 as part of a community-based, prospective study of the relation between infant feeding patterns and enterotoxigenic Escherichia coli producing heat-labile toxin (LT-ETEC) diarrheal disease. Strictly formula-fed children had an incidence of diarrhea over three times that of strictly breast-fed infants and twice that of breast-fed and supplementally fed children. Strictly formula-fed infants colonized by LT-ETEC were symptomatic for diarrhea nearly three times as often as strictly breast-fed infants and twice as often as infants receiving a mixed diet. The fitting of parametric hazard models to durations until LT-ETEC colonization revealed that the hazard for the first colonization was time invariant. The hazard of diarrhea increased by 400-500% during the rainy season or among children 3 months of age or older who received avena, a barley drink. The best-fitting hazard models to durations until symptomatic expression of LT-ETEC infection all increased through time. This hazard was inversely impacted by the overall amount of LT-ETEC-specific, immunoglobulin A antibodies the infant received via the mother's breast milk and by the provision of traditional medicinal teas.

Bacterial Toxins↗
PubMed1994

Women's reproductive cancers in evolutionary context.

Reproductive experiences for women in today's affluent Western nations differ from those of women in hunting and gathering societies, who continue the ancestral human pattern. These differences parallel commonly accepted reproductive risk factors for cancers of the breast, endometrium and ovary. Nutritional practices, exercise requirements, and body composition are nonreproductive influences that have been proposed as additional factors affecting the incidence of women's cancers. In each case, these would further increase risk for women in industrialized countries relative to forager women. Lifestyles and reproductive patterns new from an evolutionary perspective may promote women's cancers. Calculations based on a theoretical model suggest that, to age 60, modern Western women have a breast cancer risk as much as 100 times that of preagricultural women.

Biological Evolution↗
PubMed1994

A multistate model of fecundability and sterility.

This paper develops a multistate hazards model for estimating fecundability and sterility from data on waiting times to conception. Important features of the model include separate sterile and nonsterile states, a distinction between preexisting sterility and sterility that begins after initiation of exposure, and log-normally distributed fecundability among nonsterile couples. Application of the model to data on first birth intervals from Taiwan, Sri Lanka, and the Amish shows that heterogeneity in fecundability is statistically significant at most ages, but that preexisting sterility and new sterility are unimportant before age 40. These results suggest that sterility may not be an important determinant of natural fertility until later reproductive ages.

Adolescent↗
PubMed1990

Birth spacing patterns in humans and apes.

Comparative studies of birth interval dynamics in wild primates suffer from several problems of analysis and interpretation: (1) the data are always right-censored, (2) sample sizes are usually small, (3) the distribution of birth intervals is expected to be non-normal, (4) early offspring mortality is a confounding variable, and (5) differences in life history (e.g., presence or absence of menopause) can complicate interpretation of the results. A survival analysis designed to minimize these problems is applied to published data on wild chimpanzees and gorillas from Gombe and Virunga Parks, respectively, and to new data on wild orangutans from Tanjung Puting National Park and on a human population, the Gainj of highland Papua New Guinea. According to this analysis, the estimated median birth interval (when the offspring whose birth opens the interval does not die within the interval) is 43.3 +/- 1.0 months for the Gainj, 45.5 +/- 1.2 months for gorillas, 66.6 +/- 1.3 months for chimpanzees, and 92.6 +/- 2.4 months for orangutans.

Animals↗
PubMed1990

A possible mechanism of action for azelaic acid in the human epidermis.

Azelaic acid, and other saturated dicarboxylic acids (C9-C12), are shown to be competitive inhibitors of tyrosinase (KI azelaic acid = 2.73 X 10(-3) M) and of membrane-associated thioredoxin reductase (KI azelaic acid = 1.25 X 10(-5) M). The monomethyl ester of azelaic acid does not inhibit thioredoxin reductase, but it does inhibit tyrosinase, although double the concentration is necessary compared with azelaic acid (KI azelaic acid monomethyl ester = 5.24 X 10(-3) M). Neither azelaic acid nor its monomethyl ester inhibit tyrosinase when catechol is used as a substrate instead of L-tyrosine. Therefore, the weak inhibitory action of azelaic acid on tyrosinase appears to be due to the competition of a single carboxylate group on this inhibitor for the alpha-carboxylate binding site of the L-tyrosine substrate on the enzyme active site. Based on the inhibitor constant on tyrosinase, at least cytotoxic levels of azelaic acid would be required for the direct inhibition of melanin biosynthesis in melanosomes if this mechanism is responsible for depigmentation in the hyperpigmentation disorders lentigo maligna and melasma. Alternatively only 10(-5) M azelaic acid is required to inhibit thioredoxin reductase. This enzyme is shown to regulate tyrosinase through a feedback mechanism involving electron transfer to intracellular thioredoxin, followed by a specific interaction between reduced thioredoxin and tyrosinase. Furthermore, the thioredoxin reductase/thioredoxin system is shown to be a principal electron donor for the ribonucleotide reductases which regulates DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells, Cultured↗
PubMed1990

Fertility in anthropological populations.

"In this review I draw upon statistical demography and, to a lesser extent, reproductive endocrinology to formulate a coherent strategy for investigating fertility and reproduction in anthropological populations. The object, it must be emphasized, is not to reduce anthropology to demography or endocrinology, but rather to acquaint anthropologists with a powerful set of tools with which they can address issues of anthropological interest." The author first discusses the concept of natural fertility. Next, he summarizes the most significant generalizations concerning variations in fertility among preindustrial societies using the concept of proximate determinants developed by John Bongaarts. Finally, he outlines an alternative approach that might be more suited to the analysis of such fertility variations.

Anthropology↗
PubMed1987

The allelic correlation structure of Gainj- and Kalam-speaking people. II. The genetic distance between population subdivisions.

The patterning of allele frequency variability among 18 local groups of Gainj and Kalam speakers of highland Papua New Guinea is investigated using new genetic distance methods. The genetic distances proposed here are obtained by decomposing Sewall Wright's coefficient FST into a set of coefficients corresponding to all pairs of population subdivisions. Two statistical methods are given to estimate these quantities. One method provides estimates weighted by sample sizes, while the other method does not use sample size weighting. Both methods correct for the within-individual and between-individual-within-groups sums of squares. Genetic distances among the Gainj and Kalam subdivisions are analyzed with respect to demographic, geographic, and linguistic variables. We find that a demographic feature, group size, has the greatest demonstrable association with the patterning of genetic distances. The pattern of geographic distances among groups displays a weak congruence with the pattern of genetic distances, and the association of genetic and linguistic diversity is very low. An effect of differences in group size on genetic distances is not surprising, from basic theoretical considerations, but genetic distances have not often been analyzed with respect to these variables in the past. The lack of correspondence between genetic distances and linguistic and geographic differences is an unusual feature that distinguishes the Gainj and Kalam from most other tribal populations.

Alleles↗
PubMed1987

The relative efficiency of cryogens used for plunge-cooling biological specimens.

Coolants used for freezing biological specimens were tested for cooling performance in the continuous plunge mode. Results from bare thermocouples showed that ethane cooled faster than propane or a propane:pentane mixture, even when warmed to 25 K above its freezing point. Propane coolants were more efficient than Freon 22 and the slowest cooling occurred in boiling liquid nitrogen. Hydrated gelatin specimens showed similar results with ethane cooling about 33% faster than propane. Epoxy resin specimens cooled faster than hydrated gelatin specimens of similar size. Hydrated and resin specimens cooled over increasing distances as plunge velocity increased. A bare thermocouple, however, cooled over a constant distance when plunged above a critical velocity. This phenomenon may reflect vapour formation and its suppression at high plunge velocities. The rate of cooling in hydrated specimens is shown to have an absolute limit and cannot be modelled by bare thermocouples or resin specimens.

Epoxy Resins↗